The invention relates to improvements in vibratory or oscillating sieve screening devices for screening material such as ore or coal, and more particularly to an improved structure for more effectively and uniformly driving the sieve in oscillation.
Oscillating or shaking sieves are used in ore and coal preparation installations. For continuous effective operation, and in order to handle large volumes of ore and coal, it is necessary to continuously drive the screen or sieve structure in vibration or oscillation. One form of generating the oscillating drive force is by the rotation of eccentric or unbalanced weights wherein the force from the rotation of the unbalanced weights is transmitted to the sieve surface. For satisfactory operation, it is desired that the vibratory forces are distributed as uniformly as possible over the entire sieve surface. This permits feeding the ore or coal uniformly to the surface, and results in uniform screening as the material passes over the surface. Unequal vibration results in unequal screening, and attempts to compensate for such unequal vibration are difficult because feeding the material to the screen normally is done at a uniform rate, and unequal screening is almost sure to occur if unequal vibration exists across the screen.
If the sieve construction is made narrow, it is more easy to rigidify the construction to obtain uniform vibration over the width of the screen surface. However, for production of coal and ore plants, it is commercially and economically necessary to provide relatively wide sieves which have a high through-put capacity. This in turn creates problems of obtaining rigidity of the sieve for purposes of attempting to obtain uniform vibration or oscillation across the entire width of the sieve surface.
It is accordingly an object of the invention to provide an improved construction for obtaining uniform oscillation or vibration across the width of a sieve surface making it possible to use relatively wide sieves and eliminating the necessity of very heavy constructions which are made heavy to rigidify the sieve to attempt to obtain the same vibration or oscillation in the center of the sieve as occurs at the edges. This objective is accomplished by an improved support and drive arrangement which obtains substantially uniform vibration across the width of the sieve. By eliminating heavy rigidifying constructions, the cost of sieve construction is reduced, and the input power needed for the vibratory drive can be relatively reduced.
It is accordingly a further object of the invention to provide an improved sieve construction, and method of driving a sieve in vibration which attains more uniform and more effective vibration and oscillation without increasing the input vibrational driving power needed.
A further object of the invention is to improve the uniformity of screened product obtained in a coal or ore separation sieve by providing an improved drive mechanism which makes the vibration of the sieve more uniform across its width.
In accordance with the principles of the invention, the vibratory drive for the sieve includes driving the sieve from its edges in vibration and also driving it intermediate the edges with the drive forces intermediate the edges being greater than at the edges and preferably twice the forces are applied at the intermediate point in the sieves as that at the edges. The sieve member is supported by longitudinal sidewalls and by an intermediate longitudinal wall. Conveniently, the drive forces are preferably applied by oscillatory rotational eccentric unbalanced masses with the masses for the drive for the sidewalls of a given weight and the masses for the intermediate walls being substantially twice that of the sidewalls. With this arrangement, a division of several excitation zones is attained, so that over its entire surface a strong oscillation excitation is obtained wherein all of the excitation force is utilized, but by this application of forces, uniform vibration of the sieve across its width has been the unexpected result.
Other objects, advantages and features of the invention will become more apparent with the description of the preferred embodiment, as will equivalent methods and structures which are intended to be covered herein, with the preferred embodiment containing the teachings of the principles of the invention, as described and shown in the following specification and drawings, in which: